This invention relates to an apparatus and method for controlling the tension in moving yarns. More specifically, it compensates for varying tension over the time of a process and results in consistent yarn tension, which is often desirable for the next downstream process. As a further refinement on the principle of outputting a uniformly tensioned yarn at a single station is a method and apparatus for, remotely adjusting the tension of a group of tension devices simultaneously at any time during the process as well as an individual fine-tuning of the tension for each individual yarn is disclosed.
Numerous types of tension devices are known for controlling yarn tension. These include mostly devices which add constant tension to the traveling yarn and through this method reduce the percentage of the fluctuating tension. Most of those apply pressure directly to the traveling yarn, which in turn adds tension, based on the product of applied force times the friction coefficient. However, frictional forces directly applied to the yarn can damage the yarn itself Another problem with this kind of tension device is that the yarn, which is pinched between two stationary members, can cause additional irregular tension, this is especially the case if the yarn is of uneven thickness. If for example a thick place in the traveling yarn passes this pinching place, the members are forced apart, causing a tension peak due to the mass of the stationary members, resisting the opening motion of the thick place in the yarn. Another problem with a frictional tension device is the variation of the friction coefficient of the yarn. This is especially true for unevenly waxed or oiled yarns.
More sophisticated yarn tensioning systems use complex and expensive electronic means to measure the yarn tension and electronically vary the applied tension with a close-loop feedback to achieve constant output tension.
The invention disclosed in this application employs a rotating yarn whorl around which the yarn is wrapped with sufficient wrapping angle to prevent slippage between the yarn and the yarn whorl during normal operation. Tension is applied to the yarn by braking the yarn whorl through means of mechanical frictional force, electrical eddy-current and others. The disclosed invention achieves constant output tension by reducing the applied tension by the same value as the amount of upstream tension of the yarn. Since the total downstream tension is the sum of the tension upstream of the tension device and the tension added by the tension device, the downstream tension in the disclosed invention is constant.
The invention works with the principle that the tension of the upstream is used as the means to change the applied tension of the tension controller. In a preferred method the tension of the upstream yarn strand is pulling the yarn whorl partially away from a tension generating brake and through this means reduces the added tension. The geometry of the braking force is chosen in such a manner as to reduce the set tension by exactly the same amount as the tension residing in the upstream yarn strand, hence achieving constant tension in the downstream yarn strand. It is naturally understood that if the incoming yarn tension exceeds the preset tension of the tensioning system, the yarn whorl is lifted completely from the brake shoe and the full upstream tension is transmitted downstream.
Accordingly it is an object of the present invention to provide a yarn tension controller for maintaining uniform yarn tension for delivery to a downstream yarn processing station.
It is another object of the invention to provide a yarn tension controller which allows to set a desired tension level and tension uniformity downstream from the yarn tension controller.
It is another object of the invention to provide a yarn tension controller which includes means for uniformly and simultaneously setting the yarn tension on a plurality of yarns being processed.
It is another object of the invention to provide a yarn tension controller where each unit can be individually trimmed to fine-adjusted it to suit specific needs in a downstream yarn processing station.
It is another object of the invention to provide a multiple set of yarn tension controllers for which the desired tension level in all yarns can be changed simultaneously to fit a specific need in a downstream yarn processing station.
These and other objects of the present invention are achieved by providing a yarn tension controller by applying a drag force to a whorl around which the yarn is wrapped to achieve a desired tension. If the incoming strand has no tension, the full drag force is applied to the whorl. If the incoming strand has tension, the drag force is proportionally reduced.
It is an object of the invention to achieve the drag force to the whorl by mechanical means.
It is another object of the invention to achieve the drag force to the whorl by electrical means.
It is an object in the preferred embodiments disclosed below to provide a mechanical yarn tension controller, comprising a yarn guiding entrance, a pivoted yarn whorl assembly, a stationary braking means for the whorl, a tensioning pin as a force applying means and a yarn exiting guide. The yarn whorl is by itself freewheeling and the yarn whorl assembly is pivoted at it""s bearing extension. This allows the yarn whorl assembly to pivot in plane defined by the direction of the entering yarn and the rotational axis of the yarn whorl. The yarn whorl assembly is pushed away from the entering yarn by a tension pin, which presses the yarn whorl against a stationary brake shoe.
It is another object of the invention to apply a brake to a freely rotating whorl by exerting a force to a brake shoe and then reducing this force through the tension of the incoming yarn strand to achieve a constant out-put tension downstream strand.
It is another object of the invention to achieve a constant out-put tension in the yarn by a yarn tension controller, comprising a yarn guiding entrance, a yarn whorl assembly, an electromagnet which is applying a drag force to the whorl through its eddy-current, a redirection of the incoming up-stream yarn strand and a tension sensing transducer at the point of redirection of the incoming up-stream yarn strand which generates a voltage change at the electromagnet which reduces the magnetic braking force of the whorl correspondingly.
It is another object of the invention to achieve a constant out-put tension in the yarn by a yarn tension controller, comprising a yarn guiding entrance and a yarn whorl assembly and an electromagnetic braking means for the whorl. The yarn whorl is by itself freewheeling and the yarn whorl assembly is pivoted at it""s stationary bearing extension. This allows the yarn whorl assembly to pivot in the plane of the entering yarn and the yarn whorl axis. An electric transducer between the pivotal whorl assembly and the fixed body of the tension controller measures the tension in the incoming yarn strand and reduces the applied tension by the same amount.
It is another object of the invention to achieve a constant out-put tension in the yarn by a yarn tension controller, comprising a yarn guiding entrance and a yarn whorl assembly and an electromagnetic braking means for the whorl. The yarn whorl is by itself freewheeling and the yarn whorl assembly is mounted onto a flexible support strip which is deflected by the tension in the incoming yarn towards this incoming yarn strand. This flexible support strip is equipped with an electric transducer measuring its deformation and reduces the applied tension by the same amount.
It is an object of the invention to have a mechanical tension controller, where the tension force of the exiting yarn strand is perpendicular to the swinging motion of the whorl assembly so as not to influence the brake.
It is an object of the invention to have an electrical tension controller where the tension force of the exiting yarn strand is perpendicular to the measuring direction of the transducer so as not to influence the measurement of the transducer.
It is an object of the invention to have the tension force of the entering upstream portion of the yarn in opposition direction to the applied braking force of the mechanical yarn tension controller and through this method reducing the preset controller tension, resulting in a constant output tension regardless of tension fluctuations in the upstream yarn strand.
It is another object of this invention to use different geometrical force multipliers to compensate for different coefficient of friction between the brake shoe and the yarn whorl. This geometrical force multiplier can be of various designs as for example the usage of a larger whorl diameter for the brake shoe, then for the yarn, if the coefficient of friction is smaller than one. Other methods of force multiplication can be used to compensate for different friction coefficients as are well known in physics such as the application of a leverage system or applying the force in wedge form.
According to one preferred embodiment of the invention, the friction means comprises a stationary brake shoe inside of the rotating yarn whorl, a pivotal yarn whorl assembly and a force means to engage the brake shoe and the yarn whorl.
According to a preferred embodiment of the invention, the position of the brake shoe can be individually changed to alter the geometrical multiplication factor which compensates for different friction coefficient.
According to another preferred embodiment of the invention, the force means comprises a pressure responsive expandable fluid reservoir.
According to yet another preferred embodiment of the invention, the fluid reservoir comprises a tube and includes pressure adjusting means for adjusting the pressure within the reservoir. Preferably, the fluid comprises air.
According to another preferred embodiment of the invention, tension range adjustment means are provided for adjusting the range of tension applied by the friction means.
According to another preferred embodiment of the invention, an individual fine-tuning of each yarn tension controller is provided to decrease or increase the set tension applied to the individual yarn of a selected tension controller.
According to one preferred embodiment of the invention, the air tube extends to the plurality of yarn tension controllers for simultaneously and uniformly control of the force applied to the yarn at each of the plurality of yarn tension controllers by the tension shoes.
According to one preferred embodiment of the invention, the fluid pressure of all air tubes in a processing system can be automatically raised or lowered, as for example during a speed change of the process.
According to yet another preferred embodiment of the invention, the step of applying a maximum desired pre-set tension to the yarn between the yarn supply station and the yarn processing station comprises applying the tension from a single fluid filled pressure reservoir to each of the yarn tension controllers uniformly and simultaneously.
According to yet another preferred embodiment of the invention the force means to apply pressure to the brake is a spring.
According to yet another preferred embodiment of the invention the force means to apply pressure to the brake is a magnet.
According to yet another preferred embodiment of the invention the force means to apply pressure to the brake is a weight.
According to yet another preferred embodiment of the invention the force means to apply pressure to the brake is fluid pressure.